This invention relates to CMP ("chemical mechanical planarization") materials and specifically to CMP materials comprising as the abrasive alpha alumina powders.
CMP is a process that is used to prepare semiconductor products of great importance in a wide range of electronic applications. Semiconductor devices are typically made by depositing a metal such as copper in spaces between non-conductive structures and then removing the metal layer until the non-conductive structure is exposed and the spaces between remain occupied by the metal. The demands placed on the abrasive are in many ways in conflict. It must remove the metal but preferably not the non-conductive material. It must remove efficiently but not so quickly that the process cannot be terminated when the desired level of removal has been reached.
The CMP process can be carried out using a slurry of the abrasive in a liquid medium and it is typical to include in the slurry, in addition to the abrasive, other additives including oxidizing agents, (such as hydrogen peroxide, ferric nitrate, potassium iodate and the like); corrosion inhibitors such as benzotriazole; cleaning agents and surface active agents. It can also however be carried using a fixed abrasive in which the abrasive particles are dispersed in and held within a cured resin material which can optionally be given a profiled surface.
The CMP process can be applied to any layered device comprising metal and insulator layers each of which is in turn deposited on a substrate in quantities that need to be reduced to a uniform thickness and a highly uniform surface roughness (R.sub.a) level. CMP is the process of reducing the deposited layer to the required thickness and planarity. The problem is that the best material removal abrasives leave a rather unacceptably rough surface or achieve the material removal so rapidly that the desired termination point is often overshot. Those abrasives that remove material at a moderate rate may lack selectivity or leave a poor surface.
In the past these conflicting demands have been compromised by the use of relatively soft abrasives such as gamma alumina and silica. These slow down the rate of removal but are not very discriminating as between metal and non-conductive material. Alpha alumina with an average particle size of about 100 nanometers has been proposed and this is found to be very discriminating in preferentially removing metal rather than non-conductive material. Unfortunately however it is also very aggressive such that it is very difficult to avoid "dishing" which is the formation of a depression in a metal layer lying between adjacent non-conductive material structures. Dishing adversely affects the performance of the semi-conductor and is therefore considered to be very undesirable.
A need therefore exists for an abrasive that can be presented to a substrate in a CMP application that will remove metal selectively and relatively slowly such that dishing can be minimized.